Although amounts of linoleate (18:2n-6) equal to 1-2 percent of the daily caloric intake seem adequate to meet minimal human needs for essential fatty acids, Americans consume much greater amounts of this polyunsaturated fatty acid to lower serum triglycerides and cholesterol in attempts to reduce these risk factors for thrombosis and atherosclerosis. Ironically, increased levels of dietary 18:2n-6 lead to increased eicosanoid formation, and an overproduction of eicosanoids is associated with a wide range of disorders currently requiring pharmacological therapeutic moderation. Much evidence now suggests that dietary supplements of the linolenate type (n-3) fatty acids can achieve the desired lowering of serum lipids while also diminishing eicosanoid formation from 20:4n-6. The objective of this proposal is to determine the relative effectiveness of different dietary n-3 fatty acids in moderating the daily production of eicosanoids from dietary 18:2n-6 and 20:4n-6. Particular emphasis will be on the magnitude and speed of change in the composition of cellular nonesterified pool(s) of eicosanoid precursors in response to dietary fats. An important underlying hypothesis is that the nonesterified precursor pool not only receives substrates and inhibitors from endogenous esterified cellular sources for a slow basal rate of eicosanoid formation, but it also receives a widely varied input from exogenous dietary sources which may rapidly overwhelm the endogenous steady state pool compositions in a transient manner. Methods employed will be customary ones of lipid technology supplemented with advanced instrumentation for gas chromatography-mass spectrometric analysis of the urinary metabolites of eicosanoids. We will evaluate the effectiveness of orally administered n-3 type fatty acids of 18, 20 and 22 carbon chain length in moderating eicosanoid formation when mixed with either 18:2n-6 or 20:4n-6. Competition of the acids for elongation, desaturation and esterification will be deduced from short-term analyses of the non-esterified acid and acyl-CoA pools as well as from in vitro tests of acyltransferase selectivity.